The Geology and Extinct Volcanos of Central France |
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Page 6
... evidently been the theatre ; and these lacustrine strata have been cut through , worn down , and degraded by the usual denuding agencies , pluvial and fluviatile , until but small portions of them remain to tell the tale of their former ...
... evidently been the theatre ; and these lacustrine strata have been cut through , worn down , and degraded by the usual denuding agencies , pluvial and fluviatile , until but small portions of them remain to tell the tale of their former ...
Page 7
... evidently reached some way up the valley of the Loire from the junction of that river and the Allier to the neighbourhood of Roanne . The lower levels of this great valley- plain are for the most part superficially covered with alluvium ...
... evidently reached some way up the valley of the Loire from the junction of that river and the Allier to the neighbourhood of Roanne . The lower levels of this great valley- plain are for the most part superficially covered with alluvium ...
Page 8
... evidently derived . Some beds consist of a conglomerate of worn pebbles and fragments of granite , gneiss , mica - schist , porphyry , the rocks of the adjoining elevated district , but without the admix- ture of basaltic or any other ...
... evidently derived . Some beds consist of a conglomerate of worn pebbles and fragments of granite , gneiss , mica - schist , porphyry , the rocks of the adjoining elevated district , but without the admix- ture of basaltic or any other ...
Page 9
... evidently formed in situ from the disintegrated materials of the granite on which they rest , and from which they are scarcely to be distinguished . The cement is generally siliceous , and the resulting rock is some- times hard enough ...
... evidently formed in situ from the disintegrated materials of the granite on which they rest , and from which they are scarcely to be distinguished . The cement is generally siliceous , and the resulting rock is some- times hard enough ...
Page 20
... evidently occupied the vesicles formerly existing in the stone . Where the cavity is of a considerable size , it is not filled throughout with the zeolite , but a nest or hollow pouch appears , lined with the most brilliant crystals ...
... evidently occupied the vesicles formerly existing in the stone . Where the cavity is of a considerable size , it is not filled throughout with the zeolite , but a nest or hollow pouch appears , lined with the most brilliant crystals ...
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Common terms and phrases
Allier ancient appears Ardèche augite Auvergne basaltic lava base basin bed of basalt beneath breccia calcareous calcareous peperino Cantal cellular Central France chain of puys channel character Clermont clinkstone colour columnar compact composed conglomerate considerable contains covered crater crystals of augite current of lava deposits distance district domite dyke east elevation eruption evidently excavation feet felspar fissures flowed formed fragments freshwater formation geologists Gergovia gneiss gorge granitic platform Graveneire Haute Loire heights hill lacustrine lake lava lava-current Le Puy Limagne limestone marls mass matter Mezen miles Mont Dore Monts Dôme mountain neighbouring numerous observed occupied olivine Pariou peperino plain Plate plateau points Pomel prisms probably Puy de Dôme Ramond recent remarkable ridge rise river sandstone scoriæ seen side similar Sioule slope strata stream of lava substance summit surface tertiary thick tion trachyte tuff valley vast vent Vivarais volcanic cones
Popular passages
Page 5 - History of Latin Christianity ; including that of the Popes to the Pontificate of Nicholas V.
Page viii - I conceive to be the only legitimate path of geological inquiry, and begin by examining the laws of nature which are actually in force, we cannot but perceive that numerous physical phenomena are going on at this moment on the surface of the globe by which various changes are produced in its constitution and external character.
Page 210 - The leading idea which is present in all our researches, and which accompanies every fresh observation, the sound which to the ear of the student of Nature seems continually echoed from every part of her works is — Time...
Page 210 - The time that must be allowed for the production of effects of this magnitude, by causes evidently so slow in their operation, is indeed immense ; but surely it would be absurd to urge this as an argument against the adoption of an explanation so unavoidably forced upon us. The periods which to our narrow apprehension, and compared with our ephemeral existence, appear of incalculable duration, are in all probability but trifles in the calendar of nature.
Page 178 - ... older date, there occur in this part of France a multitude of volcanic cones like those in Auvergne, produced, in all probability, each by a single eruption. These cones are much more dilapidated than the majority of those near Clermont, of which chain they appear to constitute the prolongation. ' They are so thickly sown along the axis of the granitic range that separates the Loire and Allierfrom Paulhaguet to Pradelle, as generally to touch each other by their bases, and form an almost continuous...
Page 118 - ... dykes of the same rocks.* The opposite sides of each excavation generally offer corresponding sections, the same beds being visible at similar heights on both declivities, but varying occasionally in thickness. This is universally the case in all the narrower gorges near the base of the mountain, where the diminished slope caused the lavacurrents to increase in width as much as in length ; and in these situations the same bed or series of beds often extends over a surface of many square miles,...
Page 51 - ... that last sent up. Now the variety of trachyte which composes the Puy de Dome and the neighbouring domitic puys, consisting almost wholly 'of felspar, and therefore possessing the lowest possible specific gravity, and at the same time a very rude and coarse grain and highly porous structure, is precisely that species of lava which we should expect a priori, to have possessed the minimum of fluidity when protruded into the air ; * * See Considerations on Volcanos, p.
Page 216 - ... of quadrupeds, birds, and plants, Eocene, Miocene, and Pliocene, have followed in succession ; yet the region has preserved from first to last its geographical identity ; and we can still recall to our thoughts its external condition and physical structure, before these wonderful vicissitudes began, or while a part only of the whole had been completed.
Page 61 - ... across their channel, must have given birth to a lake by their stagnation ; and would probably have ended, as in the other instance, by wearing away a passage parallel to their former one, had not the hill forming their western bank, not in this instance composed of granite, but of a soft alluvial tufa, yielded, at some distance up the stream, to the excessive pressure of the dammed-up waters.
Page 207 - ... with the occasional flooding of parts of this valley and its tributary ravines by lavas emitted in the eruptive paroxysms of the volcanoes on the neighbouring heights. Even were it allowable to have recourse to vague and hypothetical conjectures, we can conceive no gradual and progressive excavating forces, other than those which are still in operation wherever rains, frosts, floods and atmospheric decomposition act upon the surface of the earth. To these agents then we must refer the effects...